Thinking, Fast and Slow

completion. His informal survey was surely not up to scientific standards of
evidence, but it provided a reasonable basis for a baseline prediction: the
prediction you make about a case if you know nothing except the category
to which it belongs. As we saw earlier, the baseline prediction should be
the anchor for further adjustments. If you are asked to guess the height of a
woman about whom you know only that she lives in New York City, your
baseline prediction is your best guess of the average height of women in
the city. If you are now given case-specific information, for example that the
woman’s son is the starting center of his high school basketball team, you
will adjust your estimate away from the mean in the appropriate direction.
Seymour’s comparison of our team to others suggested that the forecast
of our outcome was slightly worse than the baseline prediction, which was
already grim.
The spectacular accuracy of the outside-view forecast in our problem
was surely a fluke and should not count as evidence for the validity of the
outside view. The argument for the outside view should be made on
general grounds: if the reference class is properly chosen, the outside view
will give an indication of where the ballpark is, and it may suggest, as it did
in our case, that the inside-view forecasts are not even close to it.
For a psychologist, the discrepancy between Seymour’s two judgments
is striking. He had in his head all the knowledge required to estimate the
statistics of an appropriate reference class, but he reached his initial
estimate without ever using that knowledge. Seymour’s forecast from his
insidethaa view was not an adjustment from the baseline prediction, which
had not come to his mind. It was based on the particular circumstances of
our efforts. Like the participants in the Tom W experiment, Seymour knew
the relevant base rate but did not think of applying it.
Unlike Seymour, the rest of us did not have access to the outside view
and could not have produced a reasonable baseline prediction. It is
noteworthy, however, that we did not feel we needed information about
other teams to make our guesses. My request for the outside view
surprised all of us, including me! This is a common pattern: people who
have information about an individual case rarely feel the need to know the
statistics of the class to which the case belongs.
When we were eventually exposed to the outside view, we collectively
ignored it. We can recognize what happened to us; it is similar to the
experiment that suggested the futility of teaching psychology. When they
made predictions about individual cases about which they had a little
information (a brief and bland interview), Nisbett and Borgida’s students
completely neglected the global results they had just learned. “Pallid”
statistical information is routinely discarded when it is incompatible with